https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103585
--- Comment #9 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Hacking around the logic in ipa-sra that disables the transform and adding
-fwhole-program I get down to:
Performance counter stats for './a.out-bad3':
24,946.66 msec task-clock # 0.999 CPUs utilized
1,078 context-switches # 43.212 /sec
42 cpu-migrations # 1.684 /sec
71 page-faults # 2.846 /sec
96,144,941,575 cycles # 3.854 GHz
151,439,200 stalled-cycles-frontend # 0.16% frontend cycles
idle
68,072,941,085 stalled-cycles-backend # 70.80% backend cycles
idle
210,675,636,303 instructions # 2.19 insn per cycle
# 0.32 stalled cycles per
insn
9,128,994,716 branches # 365.941 M/sec
24,781,891 branch-misses # 0.27% of all branches
24.982117481 seconds time elapsed
24.909903000 seconds user
0.036031000 seconds sys
which is not bad. I think we have two ipa-sra issues
1) ipa-sra is overparanoid about not adding derefernece. First I think it is
safe for parameters that are REFERENCE_TYPE rather than POINTER_TYPE second it
should do propagation from callers to callees: it is quite easy to figure out
that a given param contains data packed to a structure only to make callee
happy.
2) since ipa-sra is run before ipa-cp it won't simplify ipa-cp (or other)
clones even if they are static symbols.
Also I think ipa-sra may consider packing multiple structures together. If
array descriptors are passed by references and built in caller it seems
pointless to pass each as separate struct. Not sure what kind of benefits to
expect here though.
